Why is my altiobuf configured as differential input missing an output?

Question

I am using Cyclone V with Quartus 18.1. I have 2 data input groups, each with a clock and 8 data signals, all differential.

Here is a sample of the verilog for clock1 and one data bit.

diff_in tck1_i (

.datain ( CKO1P ),

.datain_b ( CKO1N ),

.dataout ( tck1 )

);

diff_in d10_i (

.datain ( D1P_0 ),

.datain_b ( D1N_0 ),

.dataout ( d10 )

);

For months this has been working OK, then suddenly only clock1 and data bits d10-d13 are mapped correctly after a compile, all other bits show 2 inputs with no output on the viewer. See attached picture. Any idea what is happening?

cstub · Answer

Found the answer. It seems that more than half my design was optimized away. I solved it by inserting (*noprune*) before the destination register definition of each input signal. I'm sure it was easier to route, however...

yuanli_s_intel · Answer

Hi Craig,Meaning to say the problem is due to the regenerating of the bitstream?Thank You

cstub · Answer

Hi Bruce,

This happens after synthesis. I discovered that my design was being optimized away. I fixed by adding *noprune* to the registers that were receiving the data bits, and that prevented the removal. Still don't understand why all of a sudden, and why legitimate logic was deleted.

Thanks, Craig

yuanli_s_intel · Answer

Perhaps, the design doesn't required that much of LVDS output? or it is not declared in Quartus with that much of bus width.

Sometimes Quartus will optimize that by removing the floating pin.

Anyway, i am glad that your design is working fine now.

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Why is my altiobuf configured as differential input missing an output?

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